🔗 Share this article

Among seabirds to polar bears, primates to orangutans, various animals appear to kiss. Now, researchers propose that ancient hominins did it too – and might even have locked lips with early Homo sapiens.

Common Microbial Clues

This isn't the initial instance experts have suggested Neanderthals and Homo sapiens were intimately acquainted. Among previous studies, researchers have discovered modern people and their thick-browed cousins shared the same mouth microbe for hundreds of thousands of years after the evolutionary divergence, suggesting they exchanged oral fluids.

"Likely they were engaging in intimate contact," the researcher noted, adding that the concept aligned with research that has found people of non-African ancestry have bits of Neanderthal DNA in their genome, revealing interbreeding was occurring.

Romantic Spin

"This offers a more romantic perspective on ancient interactions," Brindle commented.

Publishing in the publication Evolution and Human Behavior, Brindle and her team report how, to investigate the historical roots of kissing, they first had to develop a description that was not restricted by how humans smooch.

Describing Kissing

"There have been some previous attempts to define a intimate act, but it's very much been human-centric, which implies that basically other animals do not engage in this. Now we understand that they probably do, it might just not look from what our intimate contact looks like," explained Brindle.

Nonetheless, she noted some actions that looked like intimate contact were distinct activities – such as the processing and transfer of food, or "mouth contact", seen in aquatic species known as certain marine animals.

Consequently the research group came up with a definition of kissing centered around friendly interactions involving intentional oral interaction with a member of the same species, with some movement of the oral area but absence of food.

Study Approach

Brindle explained they concentrated on reports of intimate behavior in primates from the African continent and Asian regions, including primates, chimpanzees and orangutans, and employed digital recordings to confirm the observations.

The researchers then integrated this data with information on the evolutionary relationships between extant and ancient types of such animals.

Evolutionary Timeline

The team propose the findings suggest kissing evolved somewhere between 21.5m and 16.9 million years ago in the predecessors of the great primates.

Placement of Neanderthals on this evolutionary lineage means it is likely they, too, indulged in a intimate act, the researchers conclude. But the behavior may not have been limited to their own species.

"The fact that humans kiss, the fact that we currently have demonstrated that ancient relatives very likely engaged, suggests that the both groups are also likely to have kissed," Brindle noted.

Biological Importance

While the evolutionary explanation is debated, Brindle explained intimate contact could be used in reproductive situations to possibly increase mating outcomes or assist in selecting between partners, while it might help reinforce bonding when practiced in a platonic way.

Another expert in the behavior of primates said that as kissing behavior was observed in a wide range of primates it made sense its roots lie deep in our evolutionary past, and an analysis of different forms of intimate behavior among a wider variety of species might extend its origins back further still.

"Behaviors that we think of as characteristics of our species, like intimate contact, are not unique to us if we examine carefully at other animals," the expert noted.

Cultural Elements

An archaeology expert explained that kissing had a cultural element as it was not common to all societies.

"Nonetheless, as people we thrive or fail on the quality of our emotional bonds, and ways of promoting trust and closeness will have been significant for eons," she said. "This could represent an concept that appears a bit incongruous to our misplaced ideas of a rather ruthless and aggressive past, but actually it ought to be expected that Neanderthals – and including them and our own species together – kissed."